Research currently in progress concerns related morphological and physiological studies on an identified cell in the abdominal nerve cord of the crayfish, the caudal photoreceptor interneuron. The caudal photoreceptor can be uniquely identified from one experiment to the next on the basis of the anamolous light sensitivity of this pair of cells. In addition to its light sensitivity, this interneuron receives direct monosynaptic input from tactile hairs and indirect polysynaptic, also of tactile origin, from other sensory regions. Direct monosynaptic input is excitatory in nature whereas the input from parallel interneurons is inhibitory. This research project is concerned with the integration of both sources of input in the production of directionally-sensitive coded spike outputs. Intracellular dye injection and intracellular electrical recording techniques are being used in these studies.